This invention relates to rotary attenuators, and particularly to a robust, inexpensive rotary attenuator and a method of making it. Various types of attenuators are known. There are, for example, the attenuators illustrated and described in the following U.S. Pat. Nos. Re. 29,018; 3,626,352; 3,702,979; 3,750,078; 3,805,209; 3,858,128; 3,984,793; 4,001,736; 4,107,634; 4,117,425; 4,146,853; 4,222,066; 4,684,905; and, 4,695,811. The disclosures of these patents are hereby incorporated herein by reference. No representation is intended by this listing that a complete search of all relevant prior art has been conducted, or that there are no better references than the above listed patents, or that any of the above listed patents is material to patentability. Nor should any such representation be inferred.
Rotary attenuators having printed wiring boards are known. The boards of these attenuators are typically constructed from alumina ceramic substrate and like low loss materials. Other rotary attenuators have conductors printed or otherwise provided on low loss ceramic. Some low loss ceramic board attenuators are known whose boards snap into the attenuator body, for example, into the rotor of the attenuator. The ceramic boards and the springs which hold them into the attenuator are rather expensive.
According to the invention, an attenuator includes a housing defining an interior. A rotor is mounted for rotation within the housing about an axis of the rotor. First electrical contacts are provided on the housing. Second electrical contacts are provided on the rotor, along with multiple printed conductor (PC) boards for engaging respective second electrical contacts. Each PC board includes an electrically relatively non-conductive substrate. A first side of each PC board is provided with electrically relatively conductive areas and electrically relatively non-conductive areas. Electrically attenuating elements are coupled together in attenuating networks with the electrically relatively conductive areas. The attenuating networks provide selected levels of attenuation. Electrical contact is selectively made between the first electrical contacts and selected attenuating networks through the second electrical contacts.
Illustratively according to the invention, the interior is generally right circular cylindrical.
Further illustratively according to the invention, the attenuator includes an index for indicating the position of rotor within housing.
Additionally illustratively according to the invention, the attenuator includes a shaft. The rotor includes a passageway for receiving the shaft. The shaft and passageway are provided with complementary features which mate when shaft is received in the passageway.
Illustratively according to the invention, the housing includes a front closure and a rear closure. At least one of the front closure and rear closure is removably attached to the housing.
Further illustratively according to the invention, the rotor includes axially oppositely facing surfaces constructed from electrically relatively non-conductive materials. The second electrical contacts are provided on the axially oppositely facing surfaces.
Additionally illustratively according to the invention, the axially oppositely facing surfaces are surfaces of resin substrates.
Further illustratively according to the invention, the attenuator includes a detent for promoting orientation of the rotor with selected ones of the second electrical contacts in electrical contact with respective first electrical contacts.
Further illustratively according to the invention, the attenuator includes at least one groove in one of the outer perimeter of the rotor and the interior of the housing, and at least one resilient, electrically relatively conductive contact strip oriented in the groove.
Illustratively according to the invention, each PC board further includes a second side which is electrically relatively conductive. One of the electrically relatively conductive areas on the first side of each PC board is electrically coupled to the second side of that respective PC board.
Additionally illustratively according to the invention, the electrically attenuating elements include surface mount resistors.
Illustratively according to the invention, the electrically attenuating elements of the attenuator are coupled between respective conductive areas.
Additionally illustratively according to the invention, the electrically attenuating elements include surface mount resistors.
Illustratively according to the invention, the rotor includes an outer surface provided with slots which extend generally radially and axially of the outer surface. Each slot is wide enough in a circumferential direction around the outer surface of rotor to receive edgewise a respective one of the PC boards.
Further illustratively according to the invention, each PC board includes an electrically relatively conductive side. Multiple strips of resilient electrically conductive material capture the radially inner edges of respective PC boards. The respective strips of resilient electrically conductive material make electrical contact with the electrically relatively conductive side of a respective respective PC board, with one of the conductive areas of a respective PC board, and with the rotor.
Additionally illustratively according to the invention, each electrically relatively non-conductive substrate includes fiber reinforced resin.
Illustratively according to the invention, the resin is fiber reinforced.
Further illustratively according to the invention, the electrically relatively non-conductive substrate includes fiber reinforced resin.
Additionally illustratively according to the invention, the fiber reinforced resin is fiberglass.
Illustratively according to the invention, the attenuator housing is constructed from extruded aluminum.
Further illustratively according to the invention, the attenuator housing is constructed from aluminum tubing.